Resin bonded abrasive article



Reissued Mar. 4, 1941 RESIN BONDED ABRASIVE ARTICLE Samuel S. Kistler,West Boylston, and Carl E. Barnes, Worcester, Mass, assignors to NortonCompany, Worcester, Mass, a corporation of Massachusetts No Drawing.Original No. 2,189,735, dated February 6, 1940, Serial No. 187,552,January 28,

1938. Renewed ctober'31, 1939.

Application for reissue September 3, 1940, Serial No. 355,220

2 Claims.

The invention relates to abrasive articles bonded with modified polymersof esters of acrylic acid and substituted acrylic acid in which thesubstituent is either methyl or chlorine.

One object of the invention is to provide an abrasive article bondedwith a harder resin of the class indicated. Another object of theinvention is to provide an abrasive article bonded with a more heatresistant resin of the class indicated, preferably softening albove 100C. Another object of the invention is to provide a grinding wheel bondedwith a synthetic resin, having some of the characteristics of shellacbonded grinding wheels. Another object of the invention is to provide agrinding wheel bonded with a synthetic resin having some of thecharacteristics of rubber. Another object of theinvention is to providea grinding wheel bonded with a synthetic resin having characteristicssuperior to either those of shellac or rubber for certain purposes andcapable of substantial duplication in its physical'properties. Anotherob-- ject of the invention is to provide a grinding wheel bonded with asynthetic resin having definite characteristics advantageous for themanufacture of grinding wheels.

Another object of the invention is to provide a grinding wheel bondedwith a synthetic resin having one or more of the followingcharacteristics: soft as compared with phenol-formaldehyde, readilycontrollable, resistant to heat as compared with shellac and rubber, andcapable of being incorporated in a wide range of products. Anotherobject of the invention is to provide a grinding wheel bonded with aresin capable of being made in difl'erent degrees of hardness for themanufacture of grinding wheels. Other objects will be in part obvious orin part pointed out hereinafter.

The invention accordingly consists in the combinations of elements andarrangements of parts as will be illustratively described herein, andthe scope of the application of which will be indicated in the followingclaims.

It is known/that the esters of acrylic acid and substituted acrylicacids, for example alpha, methyl acrylic acid and alpha chloro acrylicacid, polymerize to form transparent solids having many usefulproperties. For the manufacture of abrasive articles, however, the lowsoftening, points of these materials may be a disadvantage.

We copolymerize a monohydric alcohol ester of I acrylic or alphasubstituted acrylic acid in which the substituent is either methyl orchlorine with the allyl ester of one of these acids, with or without theaddition of acrylic or the alpha substituted acrylic acid and/or apolyhdric alcohol ester of acrylic or the alpha substituted acid. In

the various embodiments of the invention claimed herein, there is someallyl ester of acrylic or the alpha substituted acrylic acid. Asexamples of the polyhydric alcohols, we may cite ethylene glycol,diethylene glycol, triethylene glycol, glycerol, pentaglycerol,trimethylene glycol, pentaerythritol, and mannitol.

In preparing the allyl ester of acrylic or the alpha substituted acrylicacid, we may employ customary methods of esterification, such as directesterification of the acid and alcohol with or without a catalyst,alcoholysis, the reaction of the acrylic or the alpha substitutedacrylic acid chloride with an alcohol or its metallic derivative, or thereaction of the acid anhydride and an alcohol with or without theaddition of an organic base such as pyridine. It is usually preferableto include an inhibitor, such as pyrogallol, to prevent polymerization,but this must be removed before the ester can be polymerized onused forcross-linking. The polyhydric alcohol esters, if any such are used, maybe made by these same methods.

Example I Ethylene glycol dimethacrylate was prepared as follows: Twelveand four-tenths grams (0.2 mol) of ethylene glycol and eighty grams(0.80 mol) methyl methacrylate were mixed, and ten drops of concentratedsulphuric acid were added. To this solution was added one-tenth grampyrogallol. The mixture was placed in a flask with a condenser attachedand heated to 90 C. for twenty-four hours. During this period methylalcohol distills out and gives a rough in dication of the progress ofthe reaction. When all of the methyl alcohol has distilled over, thetemperature is raised and the excess methyl methacrylate is distilled011. Before the methyl methacrylate is distilled off, it is advisable toshake the product with aqueous sodium carbonate solution to eliminatethe sulphuric acid that was added as catalyst. Since some of thepyrogallol is removed by this treatment, it is desirable to add someexcess before distilling to avoid polymerization. The residue from thisdistillalinking agent. The pure ester maybe prepared by vacuumdistillation of this product.

This method outlined above'is generally applicable to 'th'e preparationof the methacrylates of the polyhydric alcohols that are-not insolublein methyl -methacrylate.

In the preparation of these cross-linking agents, it has not beennecessary -'for us to completely purify them, but three have beenobtained in a high state of purity and t-heir boiling points are givenin the following table which specifies the vapor pressure under whichthe boiling point was determined.

Compound Temperature Pressure Degrees lllillimetcrg Ethylene glycoldilncthacrylato 253 to 5 o lll'ltflfllyllll'lll trimetliaerylnte 110'lrilnctliylcne glycol trimctllacrylatcuw 130 o Example II Methylmethacrylate containing twenty per cent allyl methacrylate andone-hundredth per cent benzoyl peroxide was heated at 60 C. fortwentyfour hours. The temperature was then raised to 110 C. for a periodof twelve hours. This can be done in a mold for the manufacture of anydesired article. The product is a transparent glass-like solid and has asoftening point higher than that of unmodified polymeric methylmethacrylate.

Example III Example IV Methyl methacrylate containing fifteen per centallyl methacrylate and twenty per cent methacrylate acid andone-hundredth per cent benzoyl-peroxide is heated at 60. C. fortwentyfour hours. The temperature is then raised to 110 C. for twelvehours. The product is a stronger, more heat resistant resin thanpolymeric methyl methacrylate.

Example V Methyl methacrylate containing ten per cent allyl methacrylateand ten per cent ethylene glycol 'dimethacrylate and fifteen per centmethacrylic acid together with one-hundredth per cent benzoyl peroxideis heated at 60 C. for twenty-four hours. The temperature is then raisedto 110 C. for twelve hours. The product is very hard and heat resistant.

According to the invention, these resins are employed in the manufactureof grinding wheels and other abrasive products. Abrasive grainconsisting of any of the varieties of alumina including fused alumina,emery and corondum, or silicon carbide or diamond bort or other suitableabrasive substances such as garnet, quartz, and any of the hard carbidesmay be formed into an abrasive product such as a grinding wheel,regulating wheel, lapping wheel or segment for any of these by bondingwith these resins. Grinding 7 21,738 The impiu'e viscous ester thusobtained is suitable for use with methyl methacrylate as a crosswheelspossessing some of the characteristics of I those bonded with rubber andshellac may be produced according .to the present invention, using anyof the resins given in the preceding Examples H to V inclusive. We; willnow give specific examples for the manufactureiof grinding wheels.

, Example VI We mix sixteen hundred and fifty-six grams of suitableabrasive with three hundred and sixtyfive cubic centimeters of monomericmethyl methacrylate, one hundred and twenty-five cubic centimeters ofmonomeric allyl methacrylate, and ten cubic centimeters of methylmethacrylate containing one per cent benzoyl per-oxide catalyst. Themixture is placed in an aluminum mold consisting of a cylindrical dishhaving slightly tapering sides and a tightly fitting aluminum cover. Analuminum core of suitable dimensions is placed in the center. Placingthe cover upon the mold, we place the mold in an oven and heat to 60 C.for twenty-four hours. We then give the wheel a further baking foraperiod of ten hours at 110 C. Either before or after the final bakingabove specified, we strip the wheel from the mold. We then face and truethe wheel. The wheel so produced is satisfactory for dry snaggingwhereas a similar wheel made from methyl methacrylate alone softens andsmears on the face and does not cut freely.

Example VII Proceeding as specified in Example VI so far as the varioussteps including the heat and use of the mold are concerned, we may makea grinding wheel with sixteen hundred and fifty-six grams of suitableabrasive and the following bond mixture: three hundred and thirty cubiccentimeters of methyl methacrylate, one hundred cubic centimeters ofallyl methacrylate, fifty cubic centimeters of ethylene glycoldimethacrylate, and twenty cubic centimeters of methyl methacrylatecontaining one per cent benzoyl peroxide catalyst. This wheel is harderand more heat resistant than that in Example VI.

Example VIII For the manufacture of grinding wheels, we may prefer undersome circumstances to produce first a powdered polymer. The powder maybe made by grin-ding the massive polymer, or as follows: to one hundredand fifty cubic centimeters of allyl methacrylate and four hundred andfifty cubic centimeters of methyl methacrylate are added six-tenths gramof benzoyl peroxide. mixture is then added .to fourteen hundred cubiccentimeters of carbon tetrachloride in which it is completely miscibleand placed in a constant temperature bath at 65 C. After an inductionperiod of about five hours the copolymer, being insoluble in the carbontetrachloride, :begins to precipitate as a fine powder and is filteredofi, washed with carbon tetrachloride and dried.

Taking sixteen hundred and fifty-six grams of abrasive grain, we mix infive hundred grams of the above described powder and placed in a hotpress. We press' the mixture for thrlty minutes at a temperature ofapproximately one hundred and fifty degrees centigrade then strip fromthe mold. The wheel is then complete, the heat and pressure havingsoftened and coalesced the resin so that it forms with the abrasivegrain an integral piece.

when it is desired to make a wheel with a high bond content, itsometimes becomes desirable to wet the abrasive grain with a suitableliquid before adding the powdered bond. Such a liquid may be a viscoussolution of polymeric in monomeric methyl methacrylate.

Proceeding as heretofore outlined in Example VIII, we may make a powderfrom methyl methacrylate, allyl methacrylate and one of the esterscontaining more than one polymerizable unsaturated group per molecule orsimilar mix-.

tures as heretofore pointed out.

In the examples given, we have used only the esters'of methacrylic acid.It is to be understood, however, that alpha chloro acrylic acid may beused within the scope of this invention. Also, whereas the methyl esterof methacrylic acid is most commonly referred to, other monohydricalcohol esters, such as isopropyl, isobutyl or phenyl esters couldequally well have been used.

While we have described the production of grinding wheels made fromabrasive grains and resin alone, it is to be understood that we may alsoincorporate a wide variety of fillers. In case the resin is polymerizedin situ, the filler must not contain inhibitors that will prevent thepolymerization.

. The present patent is directed to abrasive articles. The novel methodof making grinding wheels herein disclosed together with the new novelresins are claimed in separate copending applications Serial Nos.187,549 and 187,548, filed on January 28, 1938.

It will thus be seen that there has been provided by this invention acomposition of matter and article of manufacture in which the variousobjects hereinabove set forth together with many thoroughly practicaladvantages are successfully achieved. As many possible embodiments maybe made of the above invention and as many changes might be made in theembodiment above set forth, it is to be understood that all matterhereinbefore set forth is to be interpreted as illustrative and not in alimiting sense.

We claim:

1. An abrasive body comprising abrasive grains bonded with a copolymerof compounds comprising methyl methacrylate and allyl methacrylate.

2. As an article of manufacture, an abrasive body comprising abrasivegrains bonded with a copolymer of polymerizable compounds comprising-anallyl ester of an acid selected from the group consisting of acrylicacid and its alpha substitution products in which the substituent isselected from the groupconsisting of methyl and chlorine and a differentester of a monohydric alcohol and an acid selected from the aforesaidgroup.

SAMUEL S. KISTLER. CARL E. BARNES.

